1. Field of the Invention
The present invention is generally related to temperature control during semiconductor processing, and in particular to controlling thermal reactor temperature overshoot during introduction of cold material (wafers) into a semiconductor processing chamber.
2. Brief Description of Related Developments
In contemporary semiconductor manufacturing, standard CVD/Diffusion wafer processing is engineered around constant temperature operations. The reactors or furnaces where such operations take place are equipped with temperature sensors (thermocouples). Two sets of such sensors are generally used. Spike thermocouples, located next to the heating element and profile thermocouples, located inside the process tube, are in turn, used by the reactor control system to achieve and maintain the desired processing temperature of the wafers. Modern control systems technology has resulted in significant improvements of the reactor temperature response, in terms of set point tracking accuracy and precision, uniformity (zone matching), and disturbance attenuation. However, the one aspect of control that has remained elusive has been temperature control during the introduction of cold material (wafers) into the processing chamber, often referred to as a “boat push”. There is a problematic temperature response caused by the large disturbance that a boat push has on the temperature control. Controllers tend to have problems with large overshoots for boat pushes due to the large period of time the controller is saturated trying to recover from the cold wafers passing by the profile thermocouples. Thus, it is necessary to reduce the saturation and recover from the boat push in a controlled manner. It would be helpful to reduce the thermal reactor temperature overshoot that typically occurs following the introduction of cold wafers.